Caliper type disk brakes, hydraulic or mechanical, generally provided on bicycles include a caliper having a fixed brake pad on one side of the brake disk and a movable brake pad mounted on a piston on the other side of the brake disk. The brake is actuated by a hand operated lever mounted on the handlebar of the bicycle which is connected to the caliper by a cable. Compensation for wear of the brake pads can be adjusted for on the lever and on the caliper body to vary the stroke of operation of the cable.
One type of hydraulic brake on the market is connected to the fork by two screws that are located above the axle. There is no part of the brake that goes down to the axle. To use this brake requires buying a special fork that accepts this brake. Another type of brake on the market can be adapted to most forks. This brake has an arm that goes down to the axle. However, you must disconnect the cable and a fork hose clamp to remove the wheel. The brake stays with the wheel when the wheel is removed. This is cumbersome and takes a lot of time, and special tools are required to remove the caliper.
The two types of disk brakes presently on the market have one fixed pad and one movable pad. To allow the fixed pad to move away from the disk, the brake in one case and the disk in the other are mounted on pins which matingly engage corresponding bores. The pins will cause minimal drag when a good design is well maintained. However if the design is poor or any rust or dirt get between the pins and bores, the drag will increase. Even a minimal drag will irritate and impair the power of the rider.